Spontaneous Osteonecrosis of the Knee

First reported by Alback et al. in 1968. They described a radioluscent area in the femoral condyle surrounded by a sclerotic halo and associated with a focally active bone scan. 

Believed to be an important but underestimated cause of osteoarthritis of the knee

Can occur in the medial femoral condyle, lateral femoral condyle or medial tibial plateau

Aetiology

• Unknown

• Vascular or traumatic lesions are the two main theories 

• Trauma theory:

  • elderly women, who may be relatively osteoporotic, minor trauma causes a microfracture in the subchondral bone; this allows fluids to be expressed through the articular cartilage into the subchondral bone and marrow space, creating increased interosseous pressure and pain. This increased pressure in a closed space interferes with the blood supply and initiates the cycle of compromised circulation and resultant osseous ischaemia.

Secondary causes of AVN of the knee:

1. Steroids

2. Alcohol

3. renal transplantation

4. Gaucher disease

5. haemoglobinopathies

6. Caisson disease

7. SLE

8. etc.